28 And my
tongue [lashown] shall speak [hagah] of thy
righteousness [tsedeq] and of thy praise [t@hillah] all the day [yowm] long. KJV-Interlinear
28 Then my
tongue shall tell of your righteousness and of your praise all the day long. ESV
The tongue speaks that which is in the soul. The soul contains that which it has learned. The individual learns that which he is interested in, that which he desires, that which he pursues, that which is consistent with his ultimate intentions.
And when doctrine is the substance of the soul then there is no hypocrisy, and no public display that is superficial and phony.
And so David has Bible doctrine in the soul, and possesses a legitimate life, praising God both in public as well as in private, with no inconsistency between the two.
All day long, means consistency day in and day out.
David, or any positive believer, is consistent in their spiritual pursuit and application. They do not need to be entertained in order to draw their attention to God, to Christ, or to doctrine. They are equally interested in the exciting doctrines as well as in the boring ones.
They are self-motivated and driven to learn.
They do not take days off.
They do not go on vacation away from their daily learning responsibilities.
Few, take days or weeks or months off from eating, and Bible doctrine is the food for the soul, which requires daily nourishment.
Stop eating and you will get sick, get weak, and probably die.
It is the same with your daily study.
Stop studying, or be inconsistent in your daily study and the soul gets weak, sickly, and eventually will die from the under-nourishment.
Physical food nourishes you for this life. Bible doctrine nourishes you forever.